This invention relates generally to machines for producing a reciprocating spray of material, and, more particularly, to machines of this general type used for treating a surface by blasting with an abrasive material, or by spraying with paint or a chemical cleaning agent.
In most operations in which a surface is to be treated by blasting with an abrasive grit material such as sand or metal particles, it is usually an objective to treat the surface to be blasted as uniformly as possible. Uniformity of treatment is increased if exposure to the abrasive blast is automatically controlled, and various reciprocating mechanisms have been used in grit-blasting apparatus of the prior art. However, prior attempts to provide means for reciprocating the blast nozzle in a uniform fashion have involved the use of multiple or reversible drive motors or reversible jacks. Inevitably, such reversible devices have inherently high inertia, which results in a relatively long reversal time, and consequent slowing of the nozzle travel at the end of each stroke. Moreover, grit-blasting machines of the prior art are typically very heavy and cumbersome, and are not usable at all in some environments where access is difficult or where a structure to be treated cannot support heavy loads. Similar problems exist in automatic spray-painting or chemical treatment machines which utilize a reciprocating nozzle in an attempt to provide uniform coverage of the paint or other liquid. Use of reciprocating mechanisms of the prior art usually involves substantial slowing of the movement of the nozzle at the end of each stroke, resulting in corresponding increases in exposure to the spray at these times, and consequent non-uniformity in coverage.
Another important disadvantage of both grit-blasting and paint-spraying machines of the prior art is that they present serious problems of air pollution, especially in the immediate area of their use. Although some large grit-blasting machines include some means for recovering the grit material, the relatively large weight and size of these machines precludes their use in some areas, for example in some parts of a ship, or on floating roofs of oil storage tanks.
Pollution by paint-spraying machines is also a significant problem. Moreover, there can be a substantial paint loss in windy conditions, as well as a resulting unevenness in paint coverage.
Accordingly, there is a significant need both in the grit-blasting and liquid-spraying fields for a machine with an automatically reversing mechanism which overcomes the foregoing disadvantages, and achieves substantial uniformity of coverage by the grit or spray, while also substantially reducing environmental pollution. The present invention is principally directed to these ends.